The present invention relates to an illumination system, and more particularly to an illumination system providing light from multiple locations for use with an array of imaging mirrors such as in a projection imaging system.
A typical projection display system can include a source of light, illumination optics, an image-forming device, projection optics and a projection screen. The illumination optics collect light from a light source and direct it to one or more image-forming devices. The image-forming device(s), controlled by an electronically conditioned and processed digital video signal, produces an image corresponding to the video signal. Projection optics then magnify the image and project it onto the projection screen. White light sources, such as arc lamps, in conjunction with color wheels have been used as light sources for projection display systems. However, recently light emitting diodes (LEDs) have been introduced as an alternative source of light. Some advantages of LEDs include longer lifetime, higher efficiency and superior thermal characteristics.
One example of an image-forming device frequently used in digital projection systems is a digital micro-mirror device (DMD). The main feature of a DMD is an array of rotatable micro-mirrors. The tilt of each mirror is independently controlled by the data loaded in a memory cell associated with each mirror, to steer reflected light and spatially map a pixel of video data to a pixel on a projection screen. Light reflected by a mirror in an ON state passes through the projection optics and is projected onto the screen to create a bright field. On the other hand, light reflected by a mirror in an OFF state misses the projection optics, which results in a dark field. A color image may also be produced using a DMD, such as by utilizing color sequencing or alternatively by using three DMDs, one for each primary color (red, blue and green).
Existing DMDs are configured to reflect light that originates from only one side, with the individual mirrors of the DMD being controlled to either reflect the light toward projection optics (in an ON state) or to reflect the light to an absorption area or “dump zone” (in an OFF state).